1. Field of the Invention
The present invention relates to a method for launching and recovering watercraft, and particularly to a launch and recovery system for launching watercraft from, and recovering the watercraft to, a boat or ship while the boat or ship is underway.
2. Description of the Related Art
For many years, it has been a requirement to stop a ship dead in the water (DIW) to launch watercraft at sea. However, stopping the ship dead in the water causes increased motion as a ship begins to roll in the wave trough while losing underway status. Typically, ships use davits or cranes to deploy watercraft over the ship sides using cable lines, blocks and tackles. When the watercraft are being raised or lowered in the aforementioned manner, motion of the ship is amplified and correspondingly increases the swing of the watercraft as it is suspended from the davits.
In rough seas, launching and recovery operations using the aforementioned method becomes more difficult and dangerous. Efforts have been made to develop motion compensation systems for DIW launch and recovery operations, but such compensation systems have not been able to compensate for decreased ship stability during a DIW launch or recovery attempt.
When a ship remains underway it is much more stable than in the aforementioned DIW status. Stern wave action is substantially reduced by the ship as it displaces the sea. For example, water skiers and the like are known to move into the flat area of calm sea to the rear of a pulling craft to take advantage of this effect. Similarly, it would be desirable to have a launch system capable of deploying a watercraft into the flat area “sweet spot” behind the ship.
During combat, interdiction and coastal patrol ships can easily lose their enemy by having to stop or even slow in order to launch boarding craft, and vessels launching scouting or raiding parties can become exposed to defensive fire by losing headway while making a launch or recovery. Having the ability to launch such craft safely while underway and still at speed could prove extremely valuable in many such operations at sea.
Moreover, at sea, rescue operations for seamen or passengers who have fallen overboard are very difficult. A ship is generally required to go DIW to launch a rescue craft with current techniques, which can take considerable time and distance in many instances. Thus, using related art techniques for launch and recovery, a ship's captain executes a special turn known as a “Williamson Turn” in order to return to the overboard personnel. With aids such as global positioning systems, the location can be accurately determined, but the maneuver can take so much time that a single person lost overboard can still be difficult to locate and especially in strong currents, high waves, etc. Cruise ships may be particularly susceptible to losing passengers who have fallen overboard due to the time required to turn around, get back on course, slow down, and launch a recovery boat. The ability to launch a recovery craft immediately while still underway may therefore prove to be a great benefit to rescue operations.
Traditionally, most small boat launches are done over the lee side of the ship. While combat craft have been experimenting with stern launching from ramps in recent years, nevertheless, the ship must still slow down to launch from a ramp. It remains true that the ship is most stable while underway, and the smoothest place near a ship is aft of the ship where the ship has smoothed out the surface wave action by its shear size moving through the ocean.
Thus, a launch and recovery system for launching a watercraft from a ship while still underway solving the aforementioned problems is desired.